The reflecting element is generally formed of aluminum because this material has considerable reflecting properties. This element produces optimum direction of the lamp-generated light rays towards the cooktop, on the surface of which the container is placed, so increasing the heat transmitted to this latter. In this manner the efficiency of the cooktop is optimized. However, the quantity of heat energy which can be fed to the container is limited by the reflecting element itself, which is generally the thermally weakest member of the glass ceramic cooktop.